The present invention relates to a method for separating analogous lactone-containing high-molecular weight compounds, more particularly a method for separating lactone-containing high-molecular weight compounds having different side-chains by using a nonionic adsorption resin and/or a basic active alumina
It has been known to use silver ions for separating cis-trans isomers of an unsaturated aliphatic acid having the same number of carbon atoms (J. Chromatography, 149(1978) 417-). However, it has been difficult to separate analogous compounds which are slightly and partially different in their molecular structure by usual processes, because they have the same or almost the same number of carbon atoms and accordingly are similar to each other in physical properties such as solubility in and affinity to solvents.
The inventors of the present invention have made extensive studies for finding a method for effectively separating analogous compounds resembling each other in physical properties without changing their chemical structure. Unexpectedly, they have found a method for separating lactone-containing high-molecular weight compounds having different side-chain by using a nonionic adsorption resin and an appropriate eluent and/or a basic active alumina and an appropriate eluent.
The present invention provides a method for separating a lactone-containing high-molecular weight compound comprising subjecting a mixture of a lactone-containing high-molecular weight compound having, as its side-chain, at least one of a lower alkenyl group and a lower alkoxy group and its analogous compound(s) to either one or both steps in any order of
a step (A) for adsorbing the mixture to a nonionic adsorption resin and eluting with an aqueous solvent containing silver ions, and
a step (B) for adsorbing the mixture to a basic active alumina and eluting with an organic solvent to separate each of the compounds.
Preferably, according to the present invention, both steps (A) and (B) are carried out for separating a lactone-containing high-molecular weight compound having, as its side-chains, both a lower alkenyl group and a lower alkoxy group from its analogous compound(s). Either one of steps (A) and (B) may be conducted first, but usually step (A) may preferably be conducted first.
Step (A) is preferably carried out for separating a lactone-containing high-molecular weight compound having, as its side-chain, a lower alkenyl group from its analogous compound(s).
Step (B) is preferably carried out for separating a lactone-containing high-molecular weight compound having, as its side-chain, a lower alkoxy group from its analogous compound(s).
The lactone-containing high-molecular weight compounds to which the separation method of the present invention can be applied mean those having one or more lactone rings in their molecules and having a molecular weight of about 400 or more. They may have a monocyclic, bicyclic, tricyclic or the like basic ring structure. More preferably, the number of member atoms forming said basic ring structure is 12 or more. Such monocyclic compounds include erythromycins, leucomycins, methymycins and the like. Such tricyclic compounds having a lactone ring include tricyclic compounds as shown in EP0184162; hetero atoms-containing tricyclic compounds as shown in EP0427680, EP0532088 or WO93/04680. And the preferable tricyclic compounds having a lactone ring are 1, 14-dihyroxy-12-[2-(4-hydroxy-cyclohexyl)-1-methylvinyl]-23,25-dimethoxy-13,19,21,27-tetramethyl-11,28-dioxa-4-azatricyclo[22.3.1.04.9]octacos-18-ene-2,3,10,16-tetraone (referred to as xe2x80x9cCompound Zxe2x80x9d hereinafter)(which is tacrolimus when the 17th position is substituted with allyl group and the 3rd position is substituted with methoxy group, and ascomycin when the 17th position is substituted with ethyl group and the 3rd position is substituted with methoxy group), rapamysins, or the like. Among these compounds, tricyclic compounds are preferable and Compound Z is more preferable.
The lower alkenyl group as the side chain in the lactone-containing high-molecular weight compounds may be straight-chain or branched-chain alkenyl groups having 2-6 carbon atoms such as vinyl, propenyl (allyl or 1-propenyl), butenyl, isobutenyl, pentenyl, hexenyl and the like, among which vinyl and propenyl are preferred.
The lower alkoxy groups as the side chain in the lactone-containing high-molecular weight compounds may be straight-chain or branched-chain alkoxy groups having 1-6 carbon atoms such as methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, sec-butoxy, tert-butoxy, pentyloxy, isopentyloxy, hexyloxy and the like, among which preferred are those having 1-4 carbon atoms such as methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy and the like.
Especially, the lactone-containing high-molecular weight compound to be separated according to the present invention which has at least one of the lower alkenyl group and the lower alkoxy group as the side chain is preferably one containing Compound Z as its basic chemical structure in which the lower alkenyl group is propenyl group and the lower alkoxy group is methoxy group, one containing compound Z as its base chemical structure in which the lower alkenyl group is propenyl group, or one containing Compound Z as its basic chemical structure in which the lower alkoxy group is methoxy group.
Analogous compounds to the lactone-containing high-molecular weight compound to which the separation method of the present invention is applied mean compounds having the same or substantially the same basic chemical structure as the above-described lactone-containing high-molecular weight compound but having different substituent(s) as their side-chain(s). For example, compounds analogous to the one having the lower alkenyl groups as its side chain may be those having the same basic chemical structure but having a lower alkyl group, a lower alkoxy group, a hydroxy group or the like instead of the lower alkenyl group at the same position. Such analogous compounds include those having a basic chemical structure somewhat different in other parts than the above-mentioned substitution position but exhibiting similar properties as a whole.
Particularly prefered compounds analogous to the lactone-containing high-molecular weight compound having a lower alkenyl group as its side-chain may be those having a lower alkyl group instead of the lower alkenyl group, compounds analogous to the one having a lower alkoxy group as its side-chain may be those having a hydroxy group instead of the lower alkoxy group, and compounds analogous to the lactone-containing high-molecular weight compound having a lower alkenyl group and a lower alkoxy group as its different side-chains may be those having a lower alkyl group instead of the lower alkenyl group and/or a hydroxy group instead of the lower alkoxy group.
The lower alkyl group as side-chain in the lactone-containing high-molecular weight compounds may be straight-chain or branched-chain alkyl groups having 1-6 carbon atoms such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, hexyl and the like, among which preferred are those having 1-4 carbon atoms such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl and the like.
Adsorption of the mixture containing the lactone-containing high-molecular weight compound having at least one of lower alkenyl group and lower alkoxy group as its side-chain(s) and its analogous compound(s) on the nonionic adsorption resin or the basic active alumina, and elution of the object compound from the adsorbent according to the present invention may be carried out in the following manner.
For example, in the case that a mixture of a lactone-containing high-molecular weight compound having at least one of lower alkenyl group and lower alkoxy group as its side chain and its analogous compound(s) is obtained by fermentation, the way to subject the mixture to the separation method depends on whether these compounds are produced out of bacteria, i.e., extracellularly, or whether they are produced inside bacteria, i.e., intracellularly. If they are extracellularly produced, fermentation liquid mixture is subjected to the separation method of the present invention. If the compounds are intracellularly produced, bacteria is treated with an appropriate solvent and the resultant extract liquid mixture is then subjected to the separation method of the present invention. The fermentation liquid mixture or the extract liquid mixture, as it is or after concentrated, may be poured into a column or the like filled with an adsorbent. Alternatively, the fermentation liquid or the extract liquid may be concentrated to dryness to give a residue and then the residue may be dissolved in an appropriate solvent to give a solution, which is poured into the column or the like.
If a mixture of a lactone-containing high-molecular weight compound having at least one of lower alkenyl group and lower alkoxy group as its side chain and its analogous compound(s) is obtained by synthesis, the reaction liquid or extract liquid, as it is or after concentrated, may be poured into a column or the like filled with an adsorbent. Alternatively, the reaction liquid or the extract liquid may be concentrated to dryness to give a residue and then the residue may be dissolved in an appropriate solvent to give a solution, which is poured into the column or the like.
The lactone-containing high-molecular weight compound having at least one of lower alkenyl group and lower alkoxy group as its side-chain(s) and its analogous compound(s) contained in the mixture are selectively eluted according to their affinity to the adsorbent and the eluent, and a combined eluate containing a desired compound is concentrated to dryness. Thus the desired lactone-containing high-molecular weight compound is separated.
The nonionic adsorption resin used as the adsorbent may be a polyethylene resin having a partial structure represented by the formula: 
wherein R is a hydrogen or halogen atom. Specifically, preferably used are Diaion(copyright) HP 20, Diaion(copyright) HP20SS, Sepabeads(copyright) SP207 (manufactured by Mitsubishi Chemical Corporation, Japan) or the like. For example, in the case where the basic chemical structure of the lactone-containing high-molecular weight compound is Compound Z, it is usually preferable to use Diaion(copyright) HP20SS.
For eluting the lactone-containing high-molecular weight compound adsorbed by the nonionic adsorption resin, a silver ion-containing aqueous solvent is used. As a silver salt contained in the silver ion-containing aqueous solvent, preferred is silver nitrate, silver perchlorate or the like which exists as silver ions in water, among which silver nitrate is preferred in the case where the basic chemical structure of the lactone-containing high-molecular weight compound is Compound Z, for example. The concentration of silver ions varies depending on the nature of the lactone-containing high-molecular weight compound to be separated, but it may be generally 0.059 to 1.18 mol/L, preferably 0.12 to 0.59 mol/L, more preferably 0.18 to 0.47 mol/L, most preferably 0.24 to 0.35 mol/L, in terms of Ag+.
As an aqueous medium for the silver ion-containing aqueous solvent, an aqueous acetone, an aqueous alcohol (e.g., methanol and ethanol), an aqueous acetonitrile or the like may be exemplified. For example, an aqueous acetone may preferably be used in the case where the basic chemical structure of the lactone-containing high-molecular weight compound is Compound Z.
The basic active alumina used as the adsorbent may preferably be AC12 (tradename, manufactured by Sumitomo Chemical Company, Limited, Japan) in the case where the basic chemical structure of the lactone-containing high-molecular weight compound is Compound Z, for example.
An organic solvent is used for eluting the lactone-containing high-molecular weight compound adsorbed by the basic active alumina. The organic solvent used as the eluent may be a conventional one such as ethyl acetate, acetone, dichloromethane, a mixture of chloroform and methanol, a mixture of ethyl acetate and n-hexane or the like. For example, ethyl acetate may preferably be used in the case where the basic chemical structure of the lactone-containing high-molecular weight compound is Compound Z.
The type of the eluent and, if the eluent is a mixed solvent, the mixture ratio thereof are preferably selected according to the nature of the lactone-containing high-molecular weight compound to be separated, through preliminary analysis such as thin layer chromatography (TLC) or the like.
The amount of the adsorbent is preferable 50 times larger than the weight of the lactone-containing high-molecular weight compounds in the case where the adsorbent is a nonionic adsorption resin, and preferably 70 times larger than the weight of the lactone-containing high-molecular weight compounds in the case where the adsorbent is a basic active alumina.
The flow rate SV of the eluting solvent varies depending on the particle size of the adsorbent, and may be usually about 3 to 5 mL/min. in the case of the nonionic adsorption resin and usually about 3 to 5 mL/min. in the case of the basic active alumina.
The fraction(s) containing the lactone-containing high-molecular weight compound having at least one of lower alkenyl group and lower alkoxy group as its side-chain(s) may be detected by an ultraviolet-visible detector or a differential refractive index detector, or by TLC after obtaining several fractions. Fractions containing a desired substance are combined and evaporated to dryness under reduced pressure, whereby the desired substance is purified.
Although the present invention is the separation method for a lactone-containing high-molecular weight compound having at least one of lower alkenyl group and lower alkoxy group as its side-chain(s), it is possible to further separate an analogous compound remaining from the other analogous compounds after the separation of the lactone-containing high-molecular weight compound. For example, a lactone-containing high-molecular weight compound having a lower alkoxy group as its side-chain is separated from a mixture containing the lactone-containing high-molecular weight compound and an analogous compound having substantially the same basic chemical structure and having a hydroxy group as its side-chain, and then, the invention may be applied again for separating the analogous compound by elution using a solvent having a different polarity.